Characterization of microbial souring in berea-sand porous medium with a North Sea oil field inoculum

Microbial souring (H2S production) in porous medium was investigated in an anaerobic upflow porous medium reactor at 60 degrees C using produced waters obtained from the North Sea Ninian oilfield as the inoculum. Multiple carbon sources commonly found in oil field waters (formate, acetate, propionate, iso- and n-butyrates) with inorganic sulfate as the electron acceptor were used as the substrates. Stoichiometry and the rate of souring in the reactor column were calculated. A large proportion of H2S was trapped in the column as FeS and possibly as a gas phase. Concentration gradients for the substrates (organic acids and sulfate) and H2S were generated along the column. At steady state, the highest volumetric substrate consumption and H2S production were found at the front part (inlet) of the reactor column. The average volumetric sulfate reduction rate after H2S production had stabilized was calculated to be 203 +/- 51 mg sulfate-S . l(-1). d(-1). Comparison of the results with the authors' previous work on the Alaska Kuparuk oilfield waters indicates that the two different microbial inocula (produced waters) exhibited the same experimental trends (rates and location) for souring in the experimental reactor system. This indicates that abiotic factors, as well as microbial parameters, may play an important role for microbial souring in the system.